perf: fix stack data leak

the "reserved" field was not initialized to zero, resulting in 4 bytes
of stack data leaking to userspace....

Signed-off-by: Arjan van de Ven <arjan@linux.intel.com>
Acked-by: Peter Zijlstra <a.p.zijlstra@chello.nl>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

kernel/perf_counter.c

@@ -2665,6 +2665,7 @@ static void perf_counter_output(struct perf_counter *counter, int nmi,
 		header.size += sizeof(cpu_entry);
 
 		cpu_entry.cpu = raw_smp_processor_id();
+		cpu_entry.reserved = 0;
 	}
 
 	if (sample_type & PERF_SAMPLE_PERIOD)